We might say that the rational person is the kind of person who thinks clearly. Clarity of thought might consist of the ability to avoid contradiction or perhaps the ability to derive valuable information from large, complicated sets of data. Alternatively, we might also insist that the rationality of some individual can be determined only if we also know what percentage of his decisions have turned out in his favor (or, of course, what percentage of those decisions were motivated correctly and resulted in God’s will being fulfilled).
The various attempts to conceptualize the term, by appealing to analogy, logic, accuracy, utility, spiritual alignment, or any other standard (technical or not, tenable or not) all appear to be unable to produce uniformity in belief, conduct, or desire even if every agent in society were to exert himself to the best of his ability toward that aim.
This is just to say that maximized rationality will likely never necessitate uniformity of opinion, of lifestyle, or motivation…no matter what rationality may be.
Our emotional drive (which we might categorize as psychological motivation or desire) appears to be so fundamentally different from higher-order thinking—more primal, more involuntary—that not much needs to be said about the inability of the former to be dictated by the latter. Not much explanation is needed to convince people that two equally rational individuals might very well have different sexual preferences or a different propensity toward conflict.
Conduct (or lifestyle) has a slightly different flavor in the minds of many people, however. It is commonly thought that equally rational individuals will end up having the same political views. But this must be false. Differences in psychological constitution will certainly influence the extent to which we would prefer to live in some society x over some society y. In many cases (but perhaps not all) the difference between x and y will not involve differences in consistency or accuracy. In other words, despite what might be chanted at anarcho-capitalist rallies or at sad young adult communist living room meetings, there isn’t only ONE consistent or correct societal arrangement. Sure, if we select from multiple extremes we might be able to establish that one arrangement has resulted in more capital, happiness, freedom, and better physical health . . . but eh, all of that might be irrelevant if our question really is: “Within which kind of society would you prefer to live?”
And now we’re on to beliefs.
My impression is that beliefs are thought to have the most potential for uniformity across individuals when subjected to maximized rationality, since beliefs have theoretical import. Unlike desires and actions, a belief is an attitude toward some proposition’s veracity. However, I think this offers little hope. Given that 1) differing experiences afford a different set of beliefs, 2) not everyone has the same conceptualization ability, and 3) not everyone agrees on the standards by which a belief is evaluated, it seems that we have reason to doubt that ultimate uniformity of belief is possible in imperfect subjects.
So what does all of this mean? It probably means that we should try to refrain from despising people who have arrived at different conclusions. It probably means that we should dust off the old liberal ideal of tolerance and stop pretending that we can predict what every “rational” creature will believe and prefer.